Pyrotechnic actuator equipped with a charge comprising an oxidant and a reducing agent which are separate

ABSTRACT

The technical field of the invention is that of pyrotechnic actuators having the essential function either of inflating a structure or of displacing a component by way of a ram.  
     The subject of the invention relates more specifically to a gas-generating actuator ( 1, 100 ) comprising an ignition system ( 3, 103 ) and an energetic charge.  
     The main characteristic of the actuator ( 1, 100 ) is that the charge is made up of a reducing material ( 4, 104 ) and of an oxidizing fluid ( 2, 102 ) which are separate.

The technical field of the invention is that of pyrotechnic actuators having the essential function either of inflating a structure or of displacing a component by way of a piston. The pyrotechnic actuators according to the invention are particularly suited to land vehicles for operating safety systems of the airbag type, to aerial vehicles in order, for example, to automatically open or close a hatch, and to space vehicles for inflating structures concerned with their landing.

The pyrotechnic actuators have already been covered by several patent applications.

Mention may be made of patent EP 0 550 321 which describes a pyrotechnic ram with damped travel which can be used in any type of energy-absorption system. This ram comprises a pyrotechnic gas generator, a piston, a combustion chamber for pyrotechnic matter and a back pressure chamber together with an intermediate chamber contained between the said combustion chamber and one end of the piston. A duct connects the intermediate chamber to the back pressure chamber. The gases emitted by the generator pressurize the intermediate chamber in order to oppose the movement of the piston and thus damp its travel, some of the said gases being routed via the duct towards the back pressure chamber.

Patent application FR 2 824 875 relates to a pyrotechnic actuator possessing a body, a piston and a washer retaining the said piston in the said body. Depending on the initial position of the piston in the body the actuator may either exert thrust on an object by causing the said piston to emerge from the said body, or release a mechanical component by causing the piston to retract into the said body.

The pyrotechnic actuators described in these two patents comprise energetic charges that have already been formed and which are able to be primed for combustion under the effect of accidental unforeseen influences such as, for example, a rise in temperature, the impact of a falling object, or some friction.

In the remainder of the description, the expression “in the storage position” corresponds to the phase of non-operation of the actuator.

The actuators according to the invention involve energetic charges that are separate, entailing a reducing material and an oxidizing fluid which are initially separated. In this way, in the storage position, the energetic charges cannot therefore react to an inadvertent external influence, conferring a high level of safety on the actuators according to the invention. The said actuators are therefore perfectly suited to land, aerial or space vehicles that do not tolerate any accidental ignition that could render them unserviceable, or even destroy them.

The subject of the present invention relates to a gas-generating actuator comprising an ignition system and an energetic charge, characterized in that the said charge is made up of a reducing material and of an oxidizing fluid which are separate. In other words, in the storage position, the energetic charge is not yet formed. As a preference, the reducing material is solid.

Advantageously, the reducing material is chosen from polymethyl methacrylate, cariflex, artificial and natural resins, metals and waxes.

According to a first variant of the invention, the oxidizing fluid is liquid.

Advantageously, the oxidizing fluid is chosen from oxygen peroxide and hydroxylamine nitrate.

According to a second variant of the invention, the oxidizing fluid is gaseous.

Preferably, the oxidizing fluid is a gaseous mixture consisting mainly of oxygen.

Preferably, the reducing material consists of a solid cylindrical block through which at least one duct passes longitudinally.

Advantageously, the reducing material has, passing longitudinally through it, a central duct exhibiting at least three mutually parallel longitudinal grooves uniformly distributed around the said duct.

Advantageously, the block has, passing longitudinally through it, seven mutually parallel ducts of which one is in a central position and the other six are uniformly distributed around the said central duct and are equidistant therefrom.

As a preference, the flowrate of oxidant is controlled by a pyrotechnic valve and a regulating valve which are situated between the reserve of oxidant and the reducing material. In operation, an electrical signal leads to the unlocking of the pyrotechnic valve so as to release the oxidizing fluid so that it can come into contact with the reducing material and interact therewith, the flowrate of the said oxidizing fluid being controlled by the regulating valve.

As a preference, the ignition system comprises at least one pyrotechnic initiator and a pyrotechnic booster charge, the said system being positioned in such a way that the gases emitted by the said booster charge heat the surface of the reducing material.

Advantageously, the oxidant is brought into contact with the reducing material after the surface of the said material has been heated, so as to bring about a pyrolysis reaction, and the gases thus emitted are conveyed out of the said actuator by means of an outlet pipe. In other words, it is advantageous for the surface of the reducing material to be preheated before the oxidant is brought into contact with the said material in order to give rise to a pyrolysis reaction.

Advantageously, the gases produced by the pyrolysis reaction between the reducing material and the oxidant are cooled by means of a parallel circuit comprising a cooling liquid.

As a preference, the cooling liquid consists of ethanol.

Preferably, the circuit comprises, in succession, an expansion chamber comprising the gas outlet pipe, a reserve of cooling liquid and a connecting pipe connecting the said reserve and the said outlet pipe, the said connecting pipe being fitted with a pyrotechnic valve.

Advantageously, the expansion chamber, which has a moving wall in contact with the cooling liquid, is capable of expanding under the effect of the gases produced by the pyrolysis, thereby exerting pressure on the said liquid. Thus, when the pyrotechnic valve of the connecting pipe is open, the cooling liquid, which is pressurized, flows through the said pipe to be routed towards the outlet pipe.

As a preference, the cooling liquid which flows through the connecting pipe is diffused in the outlet pipe in the form of fine droplets. In this way, the diffusion of these droplets can be likened to that which would be produced by an atomizer for cooling the gases expelled through the outlet pipe.

According to another preferred embodiment of the invention, the flowrate of oxidant is controlled by a funnelled nozzle situated between the reserve of oxidant and the reducing material.

Advantageously, the gases emitted by the pyrolysis reaction between the oxidant and the reducing material are routed towards a buffer volume opening onto a ram equipped with a piston. In this way, the gases produced during the pyrolysis reaction will pass through the buffer volume to exert pressure on the piston of the ram. The buffer volume can be likened to a depressurization chamber in the event that the ram becomes accidentally jammed and runs the risk of causing the actuator to burst. The said volume is sized to contain all of the gases produced by the pyrolysis reaction.

The actuators according to the invention have the advantage of being autonomous and of raving a small bulk by virtue of a very great simplicity of design. They can therefore easily be inserted in any type of device or object requiring the functions demanded of such actuators. In addition, they have all the advantages associated with the use of energetic charges, namely: reliability due to the control of the ignition, small bulk due to the small size of the energetic charges, and wide variation of the effects due to the diversity of the compositions that can be used for these actuators.

The detailed description of two preferred embodiments of the invention is given hereinafter with reference to FIGS. 1 to 9.

FIG. 1 is a view in longitudinal axial section of a first preferred embodiment of an actuator according to the invention.

FIG. 2 is a perspective view of the first preferred embodiment of an actuator according to the invention, having a compact geometry.

FIG. 3 is an enlarged view in longitudinal axial section of the ignition system and of the reducing block of an actuator according to the invention.

FIG. 4 is a view in longitudinal axial section of the cooling circuit of an actuator according to the invention.

FIG. 5 is a view in longitudinal axial section of a second preferred embodiment of an actuator according to the invention, equipped with a ram.

FIG. 6 is a perspective view of the second preferred embodiment of an actuator according to the invention, without the ram.

FIG. 7 is an enlarged view in longitudinal axial section of the ignition system and of the reducing block of the second preferred embodiment of an actuator according to the invention.

FIG. 8 is a perspective view of a first preferred embodiment of a block of reducing material of an actuator according to the invention.

FIG. 9 is a perspective view of a second preferred embodiment of a block of reducing material of an actuator according to the invention.

With reference to FIGS. 1 and 2, a first preferred embodiment of an actuator 1 according to the invention comprises a reserve of oxygen 2, an ignition system 3, a reducing block 4 of polymethyl methacrylate, a gas cooling circuit 5, an exhaust device 6 for the said gases and an inflatable structure 7. The reserve of oxygen 2 consists of a rigid bottle 8 containing pressurized oxygen and comprising an exhaust duct 10 for the oxygen allowing the said bottle 8 to be connected to the reducing block 4 passing beforehand through the ignition system 3. The exhaust duct 10 consists of a rigid pipe comprising a pyrotechnic valve 11 and a regulating valve 12, the pyrotechnic valve 11 being arranged upstream of the regulating valve 12 with respect to the reserve of oxygen 2. The duct 10 has a bypass duct 13 round the regulating valve 12 to ensure that oxygen can pass if the said valve 12 closes in the context of the flowrate regulating function.

With reference to FIG. 3, the ignition system 3 comprises two initiators 14, each of which is extended by a duct 15 opening onto a booster charge 16 situated in an empty space 17 delimited partially by the reducing block 4, the said empty space 17 acting as a pyrolysis chamber when the actuator 1 is in the operating phase. The two initiators 14 are situated on a plug 18 possessing a hollow central adaptor 19 intended to accommodate one end of the exhaust duct 10 connected to the reserve of oxygen 2. The said plug 18 is screwed into one of the two ends of a hollow cylindrical body 20 containing, in succession and in continuation, the booster charge 16, the pyrolysis chamber 17, the reducing block 4, an expansion chamber 21 and a cooling liquid 22. The end of the said hollow body 20 around which the plug 18 is screwed has a central bore 52. Thus, when the plug 18 is screwed in, the hollow central adaptor 19 finds itself in the continuation of the said bore 52. In this way, the said adaptor 19 and the said bore 52 contribute to the communication between the reserve of oxygen 2 and the reducing block 4, the said communication nonetheless being interrupted by the booster charge 16. The expansion chamber 21 comprises an outlet pipe 26 for the gases resulting from the pyrolysis reaction between the reducing block 4 and the oxygen. The actuator depicted in FIG. 2 has a compact form in as much as the exhaust duct 10 has two successive elbows in the same direction, so that the entity formed by the reserve of oxygen 2, the exhaust duct 10 and the hollow cylindrical body 20 overall has a “

” shape.

With reference to FIG. 8, according to a first preferred variant of the invention, the reducing block 4 a has a cylindrical shape comprising a cylindrical central duct exhibiting nine straight and longitudinal grooves 23. The said grooves 23, each of which has a rectangular cross section, are mutually parallel and are uniformly distributed around the said central duct. They give the cross section of the said duct a star-shaped outline.

With reference to FIG. 9, according to a second preferred variant of the invention, the reducing block 4 b has, passing longitudinally through it, seven mutually parallel ducts of which one, 24, is in a central position and of which the other six, 25, are uniformly arranged around the said central duct 24 and are equidistant therefrom.

With reference to FIG. 4, the cooling circuit 5 comprises a reserve of cooling liquid 22 such as, for example, ethanol, and a connecting pipe connecting the said reserve 22 to the gas outlet pipe 26. The connecting pipe 27 comprises a pyrotechnic valve 28 and originates at the opposite end of the hollow cylindrical body 20 to the one into which the plug 18 equipped with the two initiators 14 is screwed. The said connecting pipe 27 makes two successive elbows in the same direction to open into the gas outlet pipe 26. The expansion chamber 21 is delimited by a hollow cylindrical component 29 closed at one end by a flat circular face 30 and open at the other end, the said component 29 being housed in the hollow cylindrical body 20. In the storage position, the open end of the said hollow cylindrical component 29 is an abutment against an internal shoulder of the said body 20, whereas the flat circular face 30 is in contact with the cooling liquid 22. The expansion chamber 21 is partially delimited by the reducing block 4. The gas outlet pipe 26 comprises at least a pyrotechnic valve 31 situated upstream of an inflatable structure 7.

The way in which this first preferred embodiment of an actuator 1 according to the invention works follows the following steps.

An electrical signal triggers the two initiators 14 the combustion of which will initiate the booster charge 16. The gases thus generated will occupy the pyrolysis chamber 17 to heat the surface of the reducing block 4. A further electrical signal will trigger the pyrotechnic valve 11 situated on the exhaust duct 10 of the reserve of oxygen 2 to release the said oxygen into the said duct 10. Since the booster charge 16 has been burnt, it no longer impedes the passage of the oxygen which therefore comes into contact with the reducing block 4 which has been heated beforehand. A pyrolysis reaction then occurs between the oxygen and the reducing block 4. The hot gases originating from this reaction pressurize the expansion chamber 21 which will exert thrust on the cooling liquid 22. The pyrotechnic valve 28 borne by the connecting pipe 27 is then opened and the cooling liquid 22 therefore finds itself expelled from the said pipe 27 under the effect of the thrust of the expansion chamber 21. The said liquid 22 reaches the outlet pipe 26 in the form of fine droplets which will cool the hot gases escaping from the expansion chamber 21. The pyrotechnic valve 31 of the outlet pipe 26 is triggered to allow the cooled gases to escape and enter the inflatable structure 7.

With reference to FIGS. 5 and 6, a second preferred embodiment of an actuator 100 according to the invention comprises a reserve of oxygen 102, an ignition system 103, a reducing block 104 of polymethyl methacrylate, a buffer volume 140 and a ram 141 equipped with a piston 142. The reserve of oxygen 102 is stored in a hollow cylindrical component 105 having, at its two ends, a flat circular face. One of the two flat faces has a central bore acting as a filling orifice and which is blocked off by a plug 106. The other flat face comprises a central orifice 107 blocked off by a rupture disc 108, the said orifice 107 consisting of a cylindrical part extended by a conical part acting as a funnelled nozzle. The hollow cylindrical component 105 is partially screwed into a hollow cylindrical body 109 comprising the reducing block 104 and the ignition system 103. With reference to FIG. 7, the connection between the said component 105 and the said body 109 is hermetic by virtue of the insertion of two seals 110 a, 110 b between the external surface of the component 105 and the internal surface of the body 109. The component 105 is orientated in the body 109 in such a way that the flat face of the said component 105 that has a central orifice 107 blocked off by a rupture disc 108 separates the “reducing block+ignition system” entity from the reserve of oxygen 102.

The reducing block 104 is cylindrical and has a central duct possessing nine straight and longitudinal grooves. The ignition system 103 is housed in the said central duct and comprises an initiator 114 that can be triggered electrically and a gas-producing booster charge 106 which is wedged between two leaf springs 117 a, 117 b, the said booster charge 116 being extended by a nozzle 118 to allow the gases originating from the combustion of the booster charge 116 to escape under clearly defined conditions. The reducing block 104 is in abutment against an internal shoulder of the hollow cylindrical body 109 and forms an empty space 119 with the said body 109, the said space 119 being in communication with the buffer volume 140 via an outlet pipe 126. The buffer volume 140 is situated in an elongate hollow cylindrical component 143 equipped with an outlet orifice 144 connecting the said buffer volume 140 to a ram 141, the said ram 141 including a piston 142 possessing an elongate rod 146 ending in a widened head 147.

The way in which this second preferred embodiment of an actuator 100 according to the invention works is as follows. An electrical signal triggers the initiator 114 which will itself cause the combustion of the booster charge 116. The emitted gases will leave the nozzle 118 to heat the internal surface of the reducing block 104 and cause the disc 108 to burst. The pyrolysis reaction between the oxidant and the reducing block 104 generates gases which will enter the buffer volume 140 via the outlet pipe 126, then leave the said volume 140 by virtue of the outlet orifice 144 to exert pressure on the piston 142 of a ram 141 in order to displace it. 

1. Gas-generating actuator comprising an ignition system and an energetic charge, characterized in that the said charge is made up of a reducing material and of an oxidizing fluid which are separate.
 2. Actuator according to claim 1, characterized in that the reducing material is chosen from polymethyl methacrylate, cariflex, artificial and natural resins, metals and waxes.
 3. Actuator according to claim 1, characterized in that the oxidizing fluid is liquid.
 4. Actuator according to claim 3, characterized in that the oxidizing fluid is chosen from oxygen peroxide and hydroxylamine nitrate.
 5. Actuator according to claim 1, characterized in that the oxidizing fluid is gaseous.
 6. Actuator according to claim 5, characterized in that the oxidizing fluid is a gaseous mixture consisting mainly of oxygen.
 7. Actuator according to claim 1, characterized in that the reducing material consists of a solid cylindrical block through which at least one duct passes longitudinally.
 7. Actuator according to claim 7, characterized in that the block has, passing longitudinally through it, a central duct exhibiting at least three mutually parallel longitudinal grooves uniformly distributed around the said duct.
 8. Actuator according to claim 7, characterized in that the block has, passing longitudinally through it, seven mutually parallel ducts of which one is in a central position and the other six are uniformly distributed around the said central duct and are equidistant therefrom.
 9. Actuator according to claim 5, characterized in that the flowrate of oxidant is controlled by a pyrotechnic valve and a regulating valve which are situated between the reserve of oxidant and the reducing material.
 10. Actuator according to claim 1, characterized in that the ignition system comprises at least one pyrotechnic initiator and a pyrotechnic booster charge, the said system being positioned in such a way that the gases emitted by the said booster charge heat the surface of the reducing material.
 11. Actuator according to claim 11, characterized in that the oxidant is brought into contact with the reducing material after the surface of the said material has been heated, so as to bring about a pyrolysis reaction, and the gases thus emitted are conveyed out of the said actuator by means of an outlet pipe.
 12. Actuator according to claim 12, characterized in that the gases produced by the pyrolysis reaction between the reducing material and the oxidant are cooled by means of a parallel circuit comprising a cooling liquid.
 13. Actuator according to claim 13, characterized in that the circuit comprises, in succession, an expansion chamber comprising the gas outlet pipe, a reserve of cooling liquid and a connecting pipe connecting the said reserve and the said outlet pipe, the said connecting pipe being fitted with a pyrotechnic valve.
 14. Actuator according to claim 14, characterized in that the expansion chamber, which has a moving wall in contact with the cooling liquid, is capable of expanding under the effect of the gases produced by the pyrolysis, thereby exerting pressure on the cooling liquid.
 15. Actuator according to claim 5, characterized in that the flowrate of oxidant is controlled by a funnelled nozzle situated between the reserve of oxidant and the reducing material.
 16. Actuator according to claim 16, characterized in that the gases emitted by the pyrolysis reaction between the oxidant (102) and the reducing material are routed towards a buffer volume opening onto a ram equipped with a piston. 